I've had a stroke of good luck - the radiator supplier (Bisque) has been v generous and sent me a replacement valve free of charge. Well impressed as the radiator was bought in 2002!
Still haven't identified the logo though. On closer inspection it's a square with a horizontal bar and adjacent to it is a stylised letter that looks like a combination of the letters b and p overlaid onto one another formed from one line looping around and over itself.
Pegler have used a logo similar to what you are describing.
It's probably a Belmont. They use the internal compression nut.
About 30 quid each. Freebie? Bargain!
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